If all goes according to plan, the Linux 4.4 kernel merge window will end today with the release of the 4.4-rc1 kernel. As all of the major subsystem updates have already landed for Linux 4.4, here's my usual look at the highlights for this kernel cycle.As noted yesterday, Linux 4.4 is currently around 20.8 million lines or an increase of about 200 thousand lines of code/documentation and a few hundred new files after Linus accepted around 12,000 commits for this merge window. In my close monitoring of the mainline Git code and mailing lists over the past few weeks, the items of Linux 4.4 that have caught my attention include:

Graphics

- AMD Stoney support, initial graphics support for an upcoming AMD APU launch.- There are numerous AMDGPU additions for those with an AMD Carrizo, Tonga, or Fiji graphics processor. That includes enabling the AMDGPU scheduler by default, new AtomBIOS opcodes, and various fixes. Sadly, there isn't any power management support in AMDGPU for Linux 4.4 for the discrete graphics cards, but those PowerPlay patches are coming for Linux 4.5 to significantly boost the performance of this modern open-source driver.- There's a Raspberry Pi KMS driver that's finally landed after the extensive work done by Eric Anholt at Broadcom. Unfortunately for Linux 4.4, this Raspberry Pi kernel graphics driver is just for kernel mode-setting and doesn't yet handle 3D hardware acceleration or power management. Eric is still working on that acceleration code as well as the accompanying VC4 Gallium3D driver.

Are The Open-Source Graphics Drivers Good Enough For Steam Linux Gaming?

- We finally have the VirtIO VirGL DRM code! This is used in conjunction with the VirtIO VirGL code in Mesa's Gallium3D along with changes in QEMU 2.5 for providing OpenGL acceleration support to guest virtual machines over QEMU+KVM with VirtIO. VMWare and VirtualBox have long offered 3D acceleration to guest VMs and it's great that finally there is support on a fully open-source virtualization stack. Of course, it will be a while before the necessary Mesa and QEMU code trickles down in released form to distributions.- Nouveau has some re-clocking improvements, better stability, and other enhancements but nothing too jaw-dropping. There's still no hardware acceleration for the modern GeForce GTX 900 series as NVIDIA hasn't yet supplied the developers with the needed signed firmware images.- Freedreno's MSM driver has added Snapdragon 820 support as Qualcomm's newest SoC.- The Intel DRM code in Linux 4.4 is primarily about fixes and other low-level improvements. The primary benefactors of Intel's latest work continues to be Skylake and Broxton graphics hardware.- Core DRM code includes more atomic mode-setting work and other changes.

ARM

- Several 64-bit ARM updates.- More UEFI 2.5 additions that include improvements for EFI on ARM64 / AArch64.- ARM SoC and platform updates.

Networking

- A lot of good stuff including a new Realtek rtl8xxxu WiFi driver, support for non-root eBPF programs, support for persistent maps/programs with eBPF, Very High Throughput MESH support in the ath10k driver, VRF support in the IPv6 stack, and other changes.